(CNN) -- Only a fraction of the oil that normally courses through the Trans Alaska pipeline was flowing early Sunday after operators discovered a leak near Prudhoe Bay, a company spokeswoman said.

Crews making a routine inspection "found oil in the basement of a booster pump building" around 9 a.m. Saturday, according to Aleyeska Pipeline Service Company spokeswoman Michelle Egan, who said flow has been reduced by 95%.

On a typical day, 642,261 barrels of oil would pass through the pipeline.

"Crews are currently onsite to assess the situation and isolate the source of the leak," a company statement said.